<!doctype html>
<style>
div[contenteditable] {
    font: 20px/25px monospace;
    border: solid 1px green;
    padding: 5px;
}

.multicol {
    column-count: 3;
    column-gap: 0;
    column-rule: none;
    column-width: 100px;
    width: 300px;
}
</style>
<div class="multicol" contenteditable><div id="target"></div></div>
<script>
const selection = window.getSelection();
const target = document.getElementById('target');
for (let i = 0; i < 10; ++i)
  target.innerHTML += `<span id="c${i}">line ${i}<br></span>`;
selection.collapse(document.getElementById('c5').firstChild, 3);
target.focus();
</script>
